1. Field of the Invention
The present invention relates to vibration-sensing gyro having a pair of tines.
2. Description of the Related Art
Vibration-sensing gyros make the tines vibrate along a predetermined direction and detect the angular velocity in the following manner.
In the following description, it is assumed that a tine vibrates along an X axis in the plane which contains rectangular coordinate axis (X-Y plane). When the tine vibrating along the X axis rotates around a Z axis perpendicular to the X-Y plane, the angular velocity generates the Coriolis force acting on the tine along a Y axis. The Coriolis force depends upon the angular velocity. The angular velocity acting on the tine can accordingly be determined by measuring the Coriolis force indirectly as a distortion of the tine or directly using the piezoelectric effects of piezoelectric elements. A vibration-sensing gyro having a pair of tines as a tuning fork has been proposed in INTERNATIONAL LAYING-OPENGAZETTE W090/10196.
Such a vibration-sensing gyro is mounted on a vehicle to detect the yaw rate generated in turning the vehicle or record the running conditions of the vehicle.
The vibration-sensing gyro proposed in INTERNATIONAL LAYING-OPEN GAZETTE W090/10196, however, has the following drawbacks. The tines are composed of quartz crystal, and both an electrode for excitation and driving and an electrode for detecting the yaw rate are formed on each tine. These two electrodes have different purposes and thereby different electrode patterns. Each tine accordingly requires plural electrode patterns and thereby has a relatively complicated electrode structure, which makes the process or work for producing the electrodes rather complicated. Wirings leading to the respective electrodes should be arranged on one tine to prevent interference of each wiring with the other electrode. This naturally requires unfavorably complicated work and process for formation of the wirings.
Each tine should have dimensions to allow the plural electrodes to be simultaneously formed thereon, which makes the entire vibration-sensing gyro rather bulky.
In order to prevent interference of the wirings with the electrodes, only the thin wirings can be formed on the tine having the space for the plural electrodes. This unfavorably limits the voltages applicable onto the excitation electrode.
A large distortion is generated on the root of a tine during vibrations of the tine. It is accordingly preferable that both the excitation electrode and the vibration detecting electrode (electrode for detecting the yaw rate) are formed on the root of each tine in order to vibrate the tine with high efficiency and detect the vibrations of the tine with high sensitivity. Since the plural electrodes are formed on each tine, however, either the excitation electrode or the vibration detecting electrode should be disposed on the end of the tine. When the excitation electrode is formed on the end of the tine, the restricted voltage applicable onto the excitation electrode prevents the tine from vibrating with a sufficiently large amplitude. This lowers the detection sensitivity of the yaw rate based on the Coriolis force. These problems also arise in vibration-sensing gyros which vibrate a metal tine with piezoelectric elements such as PZT and detect the yaw rate.